Demand for wireless broadband access communication is trending upwards. Such systems include Local Area Network (LAN) systems and Metropolitan Area Network (MAN) systems, for example. Although new wireless systems are continually being developed, such as IEEE 802.16 wireless broadband communication systems, the amount of frequency spectrum is limited within each system while demands for increased Quality of Service (QoS) increase. As a result, more and more users are driven to use a fixed amount of bandwidth with a given quality level in any particular broadband system. This results in congestion and subsequently problems in communication latency in obtaining a communication link when entering the system. This problem is compounded for mobile communication systems, wherein a mobile station moving between cells of a broadband system will require communication overhead to deal with handovers between base stations, which interrupts communication traffic for new link acquisition procedures, resulting in even further delay or latency issues.
Specifically, during network entry and/or handover conditions in IEEE 802.16 communication systems a Mobile Station (MS) exchanges a number of Media Access Control (MAC) Management Messages with a Base Station (BS). These messages form a series of Request/Reply pairs, i.e. the MS receives a downlink messages and, as a result, generates a reply message in the uplink direction. In order to send uplink messages to the BS, the MS needs to be allocated uplink transmission opportunities by the scheduler, which resides in the BS. Scheduling decisions are made and communicated to an MS connected with a BS in time segments called frames. The size of a frame in IEEE 802.16 is variable and can range from two to twenty milliseconds. Communication resources for uplink transmissions (from the MS to the BS), can be either allocated by the scheduler unilaterally or upon the MS's request. The MS requests uplink communication resources by following a process called “Uplink Bandwidth Request” and which can take several frames to complete.
One of the factors that can significantly affect the delay associated with a communication link entry/handover is the processing speed of the MS. When the MS is able to process the messages it receives and reply to the BS faster, the overall delay could be minimized. Currently, there exists no means of the MS indicating its processing capabilities to the BS so in general the scheduler assumes that the earliest an MS can respond to a message it receives in a particular frame, is at the next frame.
Referring to FIG. 1, a base station has no knowledge of the processing power of an MS. Therefore, the BS sends (1) a downlink message to the MS and typically assumes that the MS will not be able to reply before the next frame. The MS receives the downlink message and prepares a reply message (2). The time at which the reply will be ready largely depends on its processing power. An MS may have fast processing power and finish processing the downlink message (2) and be ready to reply to the message well before the end of the present frame. However, before the MS can send the uplink message to the BS, it needs to obtain uplink communication resources. For this purpose, the MS will either perform an Uplink Bandwidth Request (which will take several frames) or alternatively the BS can allocate uplink bandwidth for the MS in an unsolicited manner, trying to predict when the MS will be ready to reply. In the situation depicted in FIG. 1 the MS has finished processing the downlink message before the end of frame, but the BS has only allocated an uplink transmission opportunity in the next frame. In general, the unsolicited uplink transmission opportunity can appear in even later frames, thus further increasing the overall delay. Once the uplink transmission opportunity appears the MS can then send the reply message (3). In the situation described here, the BS only predicts processing time without input from MS. The prediction can be inaccurate quite often, especially during network entry when not enough samples of the MS's response time are available, resulting in a too conservative prediction.
As a result, each Request/Reply pair of messages takes at least two, and possibly more, frames to be completed, even though in some cases the MS can process incoming messages and reply much earlier than the beginning of the next frame. Furthermore, the processing time at the MS can be prolonged if more messages are addressed to the MS in a particular frame (e.g. Downlink Messages 2 and 3 in FIG. 2). This is because the MS will need to decode more messages in the present frame wherein the processing power is consumed for processing the newly arrived messages, thus preventing the MS from replying fast enough.
One solution is to provide vendor specific information fields to convey the MS processing capacity to the BS. However these fields are included in messages that appear much later in the network entry process, and thus the amount of time that can be saved in limited. Also, in this case, the proposed optimizations can only be implemented when BS and MS are manufactured by the same vendor.
Therefore, a need exists for a method and apparatus that reduces the amount of latency and delay in wireless broadband communication systems, particularly in communication link entry/handover procedures. It would also be an advantage to allow Request/Reply pair messages to occur within one frame. It would also be of value to provide the BS with an indication of the processing capabilities of the MSs connected with it, so that it can differentiate between faster and slower ones, even in the case that Request/Reply pair messages cannot occur within one frame for all MSs. It would also be of benefit if the prolongation of processing time, due to additional messaging could be addressed.